He's a 1 year old rabbit and whenever I take him outside he hops on me and begs to go back in and I can't take him outside in my backyard since there's multiple cats there but what can I do?
He's probably scared. There are a lot of natural threats outside that a domesticated rabbit would be wary of. Birds of prey swoop down to grab & eat rabbits, but that fear is mitigated indoors.
He also wants a hiding spot in new areas, and won't want to be put outside in a wide, open (scary) area where he doesn't know what bunny eating monster is lurking where he can't see!